The present invention relates generally to valves and more particularly concerns a valve with a seat which will maintain its sealing relationship with a closure member of the valve under extreme heat condition that may, for example, result from a fire. The invention will be specifically disclosed in connection with a high performance butterfly valve with a seat of both metal and "soft" material construction.
When flammable liquids are used in a piping system, it is highly desirable to use a valve in that system which will maintain a sealing relationship between the valve body and a valve closure member under the extreme heat conditions that may result from a fire. When flammable liquids are used, the reasons for this objective are obvious and in many situations mandatory, for loss of a sealing relationship between the valve body and its closure member may result in a situation in which the flammable liquid travels past the valve to feed the fire. If such leakage were to occur in a fire situation, a catastrophe might result.
Despite the obvious desirability of such a valve, the prior are is devoid of totally successful fire-proof valve seats. The absence of totally successful prior art fire-proof valve seats may be attributable to the often contradictory and inconsistent requirements that are inherently placed on such valve seats. On the one hand, the seats must be effective during normal operation in which no fire is present, for it must be remembered that in most circumstances, the valve will not be subjected to fire or other ultra high temperature conditions. In normal operation, it is desirable to have what is known in the art as "bubble tight" shut-off at the valve and at the interface between the valve body and the closure member in particular. This leak tight or "bubble tight" seal can usually only be accomplished with a plastic or rubber-like valve seat. Unfortunately, plastic and rubber-like materials which perform satisfactorily as valve seats in normal operation tend to deteriorate and vaporize under the ultra high temperatures of a fire. Further, as suggested above, when a plastic or rubber-like seat material deteriorates or vaporizes, the sealing relationship may be lost and a flammable fluid may be leaked past the valve and permitted to feed any existing fire.
In recognition of the problems and limitations of plastic and rubber-like seat materials, many in the prior art have utilized metal seats which provides metal-to-metal sealing relationships with the valve closure members. Metal seats have proved particularly advantageous in fire situations as they operate much more satisfactory in an ultra high temperature environment. While much more effective under fire conditions, metal valve seats are unfortunately much less effective in normal temperature operation. The prior art has not yet, according to applicant's knowledge, provided a metal valve seat that provides "bubble tight" sealing. Further, metal valve seats often interact with valve closure members on an interference principle. When such is the case, extremely high operating torques are frequently required to move the valve closure member from its closed and sealed relationship with the valve body.
One method of overcoming the limitations of both plastic and rubber-like material seats on one hand and metal seats on the other hand, has been to use both of the materials, the plastic or rubber-like material being used to provide "bubble tight" seal during normal temperature operation and the metal seat material being used to provide a seal during ultra high temperature or fire conditions.
Exemplary of the prior art valve seats using both metal and plastic or rubber-like materials is the valve seat disclosed in U.S. Pat. No. 4,113,268. The valve seat disclosed in this mentioned patent uses a metal sealing ring with a plastic or rubber insert and a backing ring formed of rubber or other elastomeric material. The plastic or resilient insert is used to provide a "bubble tight" seal, and the metal sealing ring is used to maintain a seal (although not a "bubble tight" seal) in the event of destruction or deterioration of the plastic or resilient insert, which plastic or resilient insert serves as the primary seat in normal operation. Although a valve seat of this type may be successful in many applications, it is not without attendant disadvantages. For example, the backing ring of this design is normally formed of synthetic rubber and must necessarily be formed of an elastomeric material. One of the major problems of this type of design is that a backing ring formed of rubber or other material having the requisite properties does not necessarily function in all types of media. Like rubber and synthetic rubber, most of the other commonly used materials that exhibit the elastomeric properties necessary for successful operation of such a backing ring are subject to chemical attack by the many fluid medias. Consequently, the backing ring material must be media matched. Otherwise, the media may chemically attack and destroy the backing ring material. For example, if a synthetic rubber material were used with a hydrocarbon media, the hydrocarbon media would chemically attack the synthetic rubber material, destroying the backup ring. Leakage behind the valve seat would then result. Moreover, the operational requirements of this backup ring prohibit the use of fluorinated hydrocarbon polymeric materials, materials which are chemically inert to virtually all process fluids. A backing ring of the type disclosed in the above mentioned U.S. Pat. No. 4,113,268 formed of polytetrafluoroethylene, for example, would permanently deform or "cold flow" under pressure and would allow media leakage past the closed valve.
The necessity of media matching also has disadvantages relating to inventory supplies and increases the possibility that an improper backing ring material may inadvertently be used for a given media. It is thus highly desirable to use materials that have a broad range of application, materials that give the valve a general purpose character.
Another type of valve seat which uses a combination of metal and plastic or rubber-like materials uses a resilient metal seat material which is biased to a position avoiding contact with the valve closure member when the closure member is in the closed position. This metal seat is so biased by a soft seat material of plastic or rubber-like material which sealingly engages the valve closure member when that valve closure member is in the closed position. When subjected to a fire, the plastic rubber-like material is vaporized and the resilient force of the metal seat moves that metal seat into sealing relationship with the valve closure member.
The resiliently biased metal type seat described above has a disadvantage of permitting excessive leakage when the soft seat material is not completely destroyed or during the transition period between the sealing engagement of the plastic or rubber-like seat with the closure member and sealing engagement of the metal seat with the same closure member after destruction of the soft seat. In other words, when the plastic or rubber-like seat is only partially disintegrated, the remnants or segments of the plastic or rubber-like seat material not fully disintegrated will hold the metal seat in its non-contacting, non-sealing relationship with the closure member. This same partial disintegration of the plastic or rubber-like seat material results in a loss of sealing relationship between this soft material and the valve closure member so that neither the metal nor the soft material maintains a sealing relationship, resulting in excessive leakage past the valve.
It is therefore an object of the present invention to provide a valve seat which provides a "bubble tight" seal under normal operating condition and which also maintains a seal under the ultra high temperature conditions of a fire.
It is a further object of the present invention to provide a general purpose valve seat formed of materials suitable for use with a broad range of medias.
It is yet another object of the present invention to provide a valve seat which provides an improved sealing relationship between a metal seat component and a valve closure member.
It is still another object of the present invention to provide a valve seat with a metal component in sealing contact with a valve closure member with low torque requirements for moving the closure member out of the closed position.
It is a still further object of the present invention to provide a valve seat which is custom formed to the size and configuration of a particular closure member with which the seat will be used.
It is a still further object of the present invention to permanently deform a metal valve seat to a size and configuration which precisely matches the size and configuration of the valve closure member.
Yet another object of the present invention is to provide a bidirectional valve seat for a butterfly valve which maintains its contact with a closure disc as the disc is subjected to fluid pressures from either axial side of the disc.